The government may not compel you to become a witness against yourself in its effort to convict you. This prohibition is limited to testimonial evidence. They can:

Clip hair or nail samples

Make you give a handwriting or voice sample

Extract breath or blood samples from you

However, they can never force you to speak.

This is not always an easy right to assert. Unless you have a military or CIA career, it is neither natural nor easy to resist the exhortations of an agent of the state wearing a badge and bearing a gun, especially when they are being nice. This is not the guy at Walmart changing your oil. There is always a subtly coercive and intimidating environment that accompanies any interaction with law enforcement.

"But I have nothing to hide!”

Really? How do you know?

For example, say you are walking around Target and in a pure slip-of-mind you put a stick of deodorant in your pocket. You had no intention whatsoever to steal it – you just forgot you left it there. How would you trust a police officer, called in by Target Security, to not find “intent” where you know in your heart of hearts you had none? You don’t want it to become a question for the Jury or a Judge because at that point you are charged or, as they say, south of the V.

“I want to cooperate”

Cooperate with a lawyer representing you, not a police officer who is interviewing you. Their interests are not your interests. You are helping them, not you, and that is a mode of analysis that will never fail. The most critical stage of any criminal prosecution is the beginning. By agreeing to openly speak to an agent of the state, you considerably increase the likelihood of the state convicting you.

The most disingenuous words you will ever hear from law enforcement is "you can help yourself here" ("Why Grandma what big teeth you have!" "All the more to eat you with my dear!").

Invoking your right to remain silent cannot be used against you, so keep your mouth shut for your own sake!